Laser cleaning process for semiconductor material and the like

ABSTRACT

A laser cleaning process is disclosed for cleaning the surface of materials, such as semiconductor wafers and the like, which process can be performed at atmospheric pressure. The process includes the steps of providing a structure with a surface having undesirable contaminant particles thereon, wetting the surface with a liquid including reactive or non-reactive liquids, and irradiating the surface using photon energy with sufficient energy to remove the wetting liquid and the undesirable material.

FIELD OF THE INVENTION

[0001] The present invention pertains to processes for cleaning surfacesof material and more specifically to a process of cleaning semiconductorwafers.

BACKGROUND OF THE INVENTION

[0002] In the most common prior art cleaning methods, wet chemistry isused in conjunction with sound (ultra sonic) energy, heat and/or fluidvelocities to prepare the surface of semiconductor wafers and the like.This prior art does not provide, in all cases, adequate surface cleaningor preparation.

[0003] More recently, photonic energy has been introduced as a cleanerwith additional benefits of surface reactions and simultaneous surfacepreparation. One of these photonic energy cleaning processes, known asphotochemical, uses gas chemistries or liquids in vapor phase whichrequire the condensing of the vapors on the target material to be donein a vacuum environment. An example of this type of cleaning isdisclosed in U.S. Pat. No. 4,752,668, entitled “System for Laser Removalof Excess Material From a Semiconductor Wafer”, issued Jun. 21, 1988,the laser portion of which is incorporated herein by reference. Thisseverely limits the versatility and usefulness of the prior artprocesses and unduly complicates them. Another prior art photonic energycleaning processes, known as photothermic, uses inert process gasses toclean the surface of semiconductors or displays. An example of this typeof cleaning is disclosed in U.S. Pat. No. 5,643,472, entitled “SelectiveRemoval of Material by Irradiation”, issued Jul. 1, 1997, the laserportion of which is incorporated herein by reference. Further, theseprior art processes using lasers prohibit the use of reactive liquidsand require high laser energies to provide particle removal.

[0004] Thus, it would be highly desirable to provide a cleaning processfor surfaces of substrates, such as semiconductor wafers and the like,which is more efficient and versatile.

[0005] It is a purpose of the present invention to provide a new andimproved laser cleaning process for substrates, such as semiconductorsand the like.

[0006] It is another purpose of the present invention to provide a newand improved laser cleaning process for substrates, such assemiconductors and the like, which is highly versatile and efficient.

[0007] It is still another purpose of the present invention to provide anew and improved laser cleaning process for semiconductors and the likewith the ability to simultaneously remove surface contaminants andprevent unwanted cleaning residues.

[0008] It is a further purpose of the present invention to provide a newand improved laser cleaning process for semiconductors and the likeusing liquid so that the generation of additional thermal reactionoccurs at lower laser fluences.

[0009] It is still a further purpose of the present invention to providea new and improved laser cleaning process for semiconductors and thelike which enables the manufacturing of more complex structures withultra clean semiconductor films without the negative impact of harshchemicals to the material systems.

SUMMARY OF THE INVENTION

[0010] The above problems and others are at least partially solved andthe above purposes and others are realized in a laser cleaning processfor the surface of materials including the steps of providing astructure with a surface including thereon undesirable material to beremoved, applying a wetting liquid to the surface of the structure, andirradiating the surface, using photon energy, with sufficient energy toremove the wetting liquid and the undesirable material. The wettingliquid can include reactive or non-reactive liquids and the irradiatingstep can be performed at atmospheric pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Referring to the drawings:

[0012]FIG. 1 illustrates schematically a prior art semiconductor lineprocess for wafer polishing and cleaning;

[0013]FIG. 2 illustrates schematically a line process for substratepolishing and cleaning in accordance with the present invention;

[0014]FIG. 3 illustrates schematically a line process for substratepolishing and cleaning in accordance with the present invention;

[0015]FIG. 4 illustrates schematically a semiconductor line process forwafer polishing and cleaning in accordance with the present invention;and

[0016]FIG. 5 is a simplified general flow chart illustrating generalsteps in a process in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Turning now to the figures, FIG. 1 illustrates in a simplifiedschematic form a prior art semiconductor line process for waferpolishing and cleaning. In a first stage, designated 10, eachsemiconductor wafer 11, mounted on a chuck 12 is subjected to a chemicalmechanical polish (CMP). In the CMP process each wafer 11 is exposed todilute chemicals in which silica or similar particles are entrained.Because the CMP process is well known to those skilled in the art,further description of this process is not included herein. After theCMP process, each wafer 11 moves to a second stage, designated 13, inwhich each wafer 11 is processed through a scrub track that removesgross contamination. Scrub tracks are also well known in the cleaningart and will not be described further. Subsequent to the scrub trackprocess, wafers 11 are each moved along the line to a third stage,designated 15. Stage 15 is a spin rinse dryer (SRD) which does a finalrinse and dry process to complete the line process. Wafers 11 are thenremoved from the chucks 12 and packaged for further processing.

[0018] Referring specifically to FIG. 2, a specific example of asubstrate line process, such as a semiconductor wafer line process forwafer polishing and cleaning in accordance with the present invention isillustrated. The line process is again illustrated in a simplifiedschematic view. In a first stage, designated 20, each substrate, orsemiconductor wafer, 21, mounted on a chuck 22 is subjected to achemical mechanical polish (CMP). In the CMP process each wafer 21 isexposed to dilute chemicals in which silica or similar particles areentrained. After the CMP process, each wafer 21, now having a pluralityof contaminant particles on the surface, generated during the CMPprocess, moves to a second stage, designated 23, in which each wafer 21is processed through a scrub track that removes gross contamination.During this second stage 23, a scrub process is performed by essentiallyapplying a liquid to the surface of the semiconductor wafer, suspendingtherein the plurality of contaminant particles. Subsequently, duringthis second stage 23, a majority of this liquid having contaminantparticles entrained therein is removed. Subsequent to the scrub trackprocess of stage 23, wafers 21 are each moved along the line to a thirdstage, designated 25. Stage 25 includes a laser cleaning and dryingprocess in which photonic energy from a laser 26 is directed onto thesurface to be cleaned, e.g. the surface of wafer 21. The laser cleaningand drying process, in this specific example, replaces the SRD stepillustrated in FIG. 1. In this process the scrub track step 23 dispensesa liquid to the surface of each wafer 21 and the photonic energy oflaser 26 in step 25 removes the liquid and solids while simultaneouslydrying the surface.

[0019] Referring specifically to FIG. 3, another specific example of aline process for substrate polishing and cleaning in accordance with thepresent invention is illustrated. The line process is again illustratedin a simplified schematic view. It should be understood that whilesemiconductor wafer polishing and cleaning is disclosed in the preferredembodiment, that anticipated by this disclosure is a process forcleaning and polishing various metal substrates used in micromachining,and glass substrates, such as that utilized for lens manufacture, etc.is anticipated by this disclosure. Accordingly, the term substratematerials is intended to include semiconductor materials, metals, glass,or the like.

[0020] In a first stage, designated 30, each semiconductor wafer 31,mounted on a chuck 32 is subjected to a chemical mechanical polish(CMP). In the CMP process each wafer 31 is exposed to dilute chemicalsin which silica or similar particles are entrained. Subsequent to theCMP process of stage 30, wafers 31, having a plurality of contaminantparticles, generated during the CMP process, and now chemisorbed in theremaining liquid, are each moved along the line to a second stage,designated 35.

[0021] Stage 35 includes a laser cleaning and drying process in which anenergy source 36, such as a photonic energy source, such as a laser asillustrated here, an ion energy source, such as an ion beam, or aneutralized ion energy source is directed onto the surface to becleaned, e.g. the surface of wafer 31. The cleaning and drying process,in this specific example, replaces both the scrub process and the SRDstep illustrated in FIG. 1. In this example, the CMP process of step 30dispenses a liquid to the surface of each wafer 31 and the photonicenergy of laser 36 in step 35 removes the liquid and solids whilesimultaneously drying the surface. It should be understood that duringthe irradiation stage 35 that a single process step is undertakenwhereby the surface of the substrate material is irradiated by movingthe energy source relative to the surface of the substrate material, orvice versa, so as to irradiate the entire surface of the substrate in acontinuous manner. It is anticipated by this disclosure that dependentupon the illumination size of the energy source and the size of thesurface area to be irradiated, that the entire surface can be irradiatedwithout the need to move either the energy source or the surface of thesubstrate relative to one another.

[0022] Turning now to the figures, FIG. 4 illustrates in a simplifiedschematic form a semiconductor line process for wafer polishing andcleaning. In a first stage, designated 40, each semiconductor wafer 41,mounted on a chuck 42 is subjected to a chemical mechanical polish(CMP). In the CMP process each wafer 41 is exposed to dilute chemicalsin which silica or similar particles are entrained. Because the CMPprocess is well known to those skilled in the art, further descriptionof this process is not included herein. After the CMP process, eachwafer 41 moves to a second stage, designated 43, in which each wafer 41is processed through a scrub track that removes gross contamination.Scrub tracks are also well known in the cleaning art and will not bedescribed further. Subsequent to the scrub track process, wafers 11 areeach moved along the line to a third stage, designated 45. Stage 45 is acaustic bath process in which wafer 42 is washed in a caustic solutionfor the removal of specific materials which have accumulated from othersteps or through natural occurrences. A stage 46 generally follows stage44. Stage 46 is a spin rinse dryer (SRD) which does a final rinse anddry process to complete the line process. Wafers 41 are then removedfrom the chucks 42 and packaged for further processing.

[0023] It will be understood that the semiconductor line processillustrated in FIG. 4, is intended to illustrate the use of stage 43,the caustic bath process, in accordance with the present invention.Also, while a laser dry and cleaning stage 47 is illustrated asfollowing stage 46, the spin rinse dryer stage, it should be understoodthat stage 46 is optional and stage 47 could follow stage 44 directly.Also, stages 40 and 43 are optional, at least in some applications.

[0024] Turning now to FIG. 5, a simplified general flow chart isillustrated showing general steps in a process in accordance with thepresent invention. The general steps include a first step 50 in whichthe surface to be cleaned is prepared by applying a liquid directly tothe work surface. The liquid can be either reactive or non-reactive andis applied in a non-vaporous (liquid) form. More particularly, it isdisclosed that the liquid can be reactive or non-reactive to thesubstrate surface, and/or reactive or non-reactive to the contaminantparticles. Further, the liquid can be applied directly to the surface orit can be already present from a prior step. It should be understoodthat a plurality of contaminant particles present on the semiconductorsurface (previously described) will become entrained in the liquid oncethe liquid is present. The amount of liquid can be copious or minimal,in which copious amounts can be reduced in a second step, designated 52,to a residual layer 53 of liquid of a specified minimal thickness, priorto the application of energy source by spinning, evaporation, etc. Itshould be noted that typically copious amounts of liquid havingcontaminant particles entrained therein, are left remaining on asubstrate, or wafer surface, subsequent to CMP processing steps. Toreduce this copious amount of liquid to residual layer 53 of liquidhaving contaminant particles entrained therein, the majority, and morespecifically substantially the entire surface, of the wafer is dried byspinning the wafer in the horizontal plane so that residual layer 53having a thickness of less than 20 Å, and preferably less than 10 Å isleft remaining on a majority of the wafer surface, thus leaving thedesired amount of liquid on the surface prior to the step of irradiatingthe surface. Alternatively, evaporation techniques may be used to formresidual layer 53 of the specified thickness, thus leaving the desiredamount of liquid on the surface prior to the step of irradiating thesurface. Residual layer 53 of liquid that is left remaining is disclosedand defined herein as including a layer of liquid having a thickness ofless than 20 Å, and preferably less than 10 Å. Residual layer 53remaining is characterized as a monolayer of molecules that are adsorbedon the surface having contaminant particles chemisorbed or adsorbedtherein. This process of removing the majority of the liquid from thesurface of the substrate, or wafer, prior to the irradiation step,provides for remaining residual layer 53 of liquid of a specificthickness to be left on the surface of the wafer. Residual layer 53 mustbe of a specific minimal thickness to enable the radiation to properlyevaporate the liquid in a sort of explosive fashion, thereby removingthe remaining liquid and contaminant particles from the wafer surface.It should be understood that it is anticipated by this disclosure thatresidual layer 53 may be formed as either a continuous layer or adiscontinuous layer, across the surface of the semiconductor wafer.Therefore it is disclosed that residual layer 53 covers a majority ofthe semiconductor wafer surface. It should further be understood that,depending upon wetting step 50, step 52 may or may not be included inthe process.

[0025] In a next step, designated 55, the surface to be cleaned isirradiated, using an energy source, with sufficient energy to removeresidual layer 53 of wetting liquid and the entrained contaminantparticles in a single irradiation process. It is disclosed thatanticipated by this disclosure are various energy sources, includingphoton energy sources, such as any electromagnetic waves, including butnot limited to x-ray, IR, RF, gamma, visible, such as laser, or thelike. In addition, ion energy sources, such as ion beam sources, andneutralized ion beam sources, are anticipated. In the processillustrated in FIG. 5, the energy is provided by directing the output ofa energy source 56 onto a reflecting surface 57 for imaging onto thedesired surface. Step 55 is performed at atmospheric pressure since therapid drying of the liquid on the surface results in contaminationremoval, while promoting excellent surface conditions. Using the laserto remove the liquid directly provides the ability to simultaneouslyremove surface contaminants and prevent unwanted cleaning residuals. Inthis particular embodiment, the irradiation step, and more particularly,the laser irradiation step, is carried out in a single process stepacross the entire surface area of the wafer, whereby the laserirradiation is commenced subsequent to the removal of the copious amountof liquid (as previously described) to leave remaining residual layer 53of the liquid having entrained therein contaminant particles on amajority of the wafer surface. The laser also enhances chemicalreactions within a zone surrounding the laser beam. The reactions arecontained at or near the surface to be cleaned, which provides a greatdeal of controllability of the reactions. Further, by using liquid atthe surface to be cleaned, the generation of additional thermal reactionat lower laser fluences is realized. The use of liquid on the surfaceand direct laser cleaning lessens the quantity of chemicals used in thecleaning process and the post treatment of the chemicals.

[0026] Generally, the new process includes applying a liquid to thesurface to be cleaned at the laser stage, applying liquid to the surfaceto be cleaned prior to the laser stage, or applying liquid to thesurface to be cleaned prior to the laser stage and performing acontrolled spin to leave a controlled amount of liquid, the residuallayer, on the surface. Further, while many cleaning applications arepossible, three preferred examples in semiconductor processing are:removal of polishing slurries; enhanced removal of photo resists; andsurface preparation prior to film depositions.

[0027] Thus, a new and useful cleaning process for semiconductors andthe like is disclosed. The new and improved cleaning process forsemiconductors and the like is highly versatile and efficient with theability to simultaneously remove surface contaminants and preventunwanted cleaning residues. Further, the new and improved cleaningprocess for semiconductors and the like uses liquid directly on thesurface to be cleaned so that the generation of additional thermalreaction occurs at lower laser fluences. Also, the new and improvedcleaning process for semiconductors and the like enables themanufacturing of more complex structures with ultra clean semiconductorfilms without the negative impact of harsh chemicals to the materialsystems.

[0028] While we have shown and described specific embodiments of thepresent invention, further modifications and improvements will occur tothose skilled in the art. We desire it to be understood, therefore, thatthis invention is not limited to the particular forms shown and weintend in the appended claims to cover all modifications that do notdepart from the spirit and scope of this invention.

What is claimed is:
 1. A cleaning process for a surface of asemiconductor wafer having undesirable materials thereon, comprising thesteps of: performing a chemical mechanical polish on the surface of thesemiconductor wafer, thereby generating a plurality of contaminantparticles on the surface of the semiconductor wafer; performing a scrubby applying a liquid to the surface of the semiconductor wafersuspending therein the plurality of contaminant particles, and removinga majority of the liquid and contaminant particles suspended therein;removing a majority of the remaining liquid and contaminant particlessuspended therein so that only a residual layer of the liquid having athickness of less than 20 angstroms, and having contaminant particlessuspended therein remains on a majority of the wafer surface; andirradiating the residual layer of liquid with energy to remove theremaining residual layer.
 2. The cleaning process for the surface of thesemiconductor wafer of claim 1 wherein the step of performing scrubincludes the step of using a liquid that is one of reactive with thesurface or reactive with the particles.
 3. The cleaning process for thesurface of the semiconductor wafer of claim 1 wherein the step ofperforming a scrub includes the step of using a liquid that is one ofnon-reactive with the surface or non-reactive with the particles.
 4. Thecleaning process for the surface of the semiconductor wafer of claim 1wherein the step of removing a majority of the liquid so that only aresidual layer of the liquid remains on the wafer surface comprises thestep of spinning.
 5. The cleaning process for the surface of thesemiconductor wafer of claim 1 wherein the step of removing a majorityof the liquid so that only a residual layer of the liquid remains on thewafer surface comprises evaporation.
 6. A laser cleaning process for asurface of a semiconductor wafer of claim 1 wherein the residual layeris less than 10 angstroms thick.
 7. A laser cleaning process for asurface of a semiconductor wafer of claim 6 wherein the residual layeris a monolayer of molecules adsorbed on the surface of the semiconductorwafer, having the contaminant particles chemisorbed therein.
 8. A lasercleaning process for a surface of a semiconductor wafer of claim 6wherein the residual layer is a monolayer of molecules adsorbed on thesurface of the semiconductor wafer, having the contaminant particlesadsorbed therein.
 9. A laser cleaning process for a surface of asemiconductor wafer of claim 1 wherein the energy source is one of aphoton energy source or an ion energy source.
 10. A cleaning process fora surface of a semiconductor wafer having undesirable materials thereon,comprising the steps of: performing a chemical mechanical polish on thesurface by applying a liquid thereto, thereby generating a plurality ofcontaminant particles on the surface; removing a majority of the liquidhaving the plurality of contaminant particles chemisorbed therein sothat only a residual layer of the liquid having a thickness of less than20 angstroms remains on the wafer surface; and irradiating the remainingresidual layer of liquid with energy to remove the remaining residuallayer.
 11. The cleaning process for the surface of the semiconductorwafer of claim 10 wherein the step of performing a chemical mechanicalpolish includes the step of using a liquid that is one of reactive withthe surface or reactive with the particles.
 12. The cleaning process forthe surface of the semiconductor wafer of claim 10 wherein the step ofperforming a chemical mechanical polish includes the step of using aliquid that is one of non-reactive with the surface or non-reactive withthe particles.
 13. The cleaning process for the surface of thesemiconductor wafer of claim 10 wherein the step of removing a majorityof the liquid so that only a residual layer of the liquid remains on thewafer surface comprises the step of spinning.
 14. The cleaning processfor the surface of the semiconductor wafer of claim 10 wherein the stepof removing a majority of the liquid so that only a residual layer ofthe liquid remains on the wafer surface comprises evaporation.
 15. Alaser cleaning process for a surface of a semiconductor wafer of claim10 wherein the residual layer is less than 10 angstroms thick.
 16. Alaser cleaning process for a surface of a semiconductor wafer of claim15 wherein the residual layer is a monolayer of molecules adsorbed onthe surface of the semiconductor wafer, having the contaminant particleschemisorbed therein.
 17. A laser cleaning process for a surface of asemiconductor wafer of claim 15 wherein the residual layer is amonolayer of molecules adsorbed on the surface of the semiconductorwafer, having the contaminant particles adsorbed therein.
 18. A lasercleaning process for a surface of a semiconductor wafer of claim 10wherein the energy source is one of a photon energy source or an ionenergy source.
 19. A laser cleaning process for a surface of asemiconductor wafer having undesirable materials thereon, comprising thesteps of: performing a chemical mechanical polish on the surface of asemiconductor wafer by applying liquid thereto, thereby generating aplurality of contaminant particles chemisorbed within the liquid;removing a majority of the liquid by spinning the wafer in thehorizontal plane so that only a residual layer of liquid characterizedas a monolayer of molecules adsorbed on the surface and having theplurality of contaminant particles chemisorbed therein remains on theentire wafer surface; and irradiating the remaining residual layer ofliquid with photon energy from the laser to remove the remainingresidual layer of liquid and contaminant particles.
 20. A laser cleaningprocess for a surface of a semiconductor wafer having undesirablematerials thereon, as claimed in claim 19 further including the step ofperforming a scrub and removing a majority of the liquid and particlesprior to removing a majority of the liquid by spinning.
 21. A lasercleaning process for a surface of a substrate having undesirablematerials thereon, comprising the steps of: performing a chemicalmechanical polish on the surface of the substrate, thereby generating aplurality of contaminant particles on the surface of the substrate;performing a scrub by applying a liquid to the surface of the substratesuspending therein the plurality of contaminant particles, and removinga majority of the liquid and contaminant particles suspended therein;removing a majority of the remaining liquid and contaminant particlessuspended therein so that only a residual layer of the liquid having athickness of less than 10 angstroms and having contaminant particlessuspended therein remains on a majority of the wafer surface; andirradiating the residual layer of liquid with photon energy from thelaser to remove the remaining residual layer.
 22. A laser cleaningprocess for a surface of a semiconductor wafer of claim 21 wherein thesubstrate is one of a semiconductor wafer, a metal, or a glass.
 23. Alaser cleaning process for a surface of a semiconductor wafer of claim21 wherein the residual layer is a monolayer of molecules adsorbed onthe surface of the semiconductor wafer, having the contaminant particleschemisorbed therein.
 24. A laser cleaning process for a surface of asemiconductor wafer of claim 21 wherein the residual layer is amonolayer of molecules adsorbed on the surface of the semiconductorwafer, having the contaminant particles adsorbed therein.